The conventional devices for testing open/short of printed circuit boards generally include flying probe tester, universal tester and dedicated tester.
The flying probe tester is commonly used for testing small quantities of printed circuit boards, while the remaining testers are used for large quantities. The universal tester is expensive itself but it uses a test fixture that is less expensive. On the contrary, the dedicated tester is cheap but requires a test fixture that is expensive.
The dedicated testing chooses points to be tested according to circuit layout of a tested printed circuit board and chooses proper spring probes according to the size of the points to be tested and the distance between adjacent points to be tested. Two principles are employed in choosing the spring probes: (1) whether or not, the spring probes include features suitable to test the points; (2) after the receptacles of the probes inserted in the fixing board of test fixture, no short circuit happened. The diameters of receptacles for the spring probes are within the range between 0.45 m/m to 1.65 m/m.
The process for making the conventional dedicated testing is to choose proper points to be tested and the diameters of the probes, drilling holes in the fixing board with proper diameters according to the diameters of the receptacles. The coordinates of holes and points to be tested are the same. Each hole is inserted with a receptacle. The holes for connectors are defined at a side of the fixing board and connectors are inserted in the holes. The number of the pins of the connectors has to be larger than or equal to the number of the probes. Conductive wires are wound between the pins and the receptacles pair by pair, and each receptacle is inserted with a probe.
When using the dedicated tester, the test fixture has to be fixed to the press of the tester and the connectors on the test fixture are connected to the tester with flat cables so that each probe is connected to a test node in the tester. When the press is lowered, the spring in the probe is applied by a force so that the plunger of the probe and the point to be tested on the printed circuit board are electrically connected so that the points to be tested on the printed circuit board become conductive with the test node in the tester because of close contact. This can be used to test the open/short of each trace of the layout.
The spring probe is a contact tool with a complicated structure including a receptacle, a barrel, a plunger and a spring between plunger and barrel. It is difficult to make a small size spring probe, which is expensive and has a short service life. The conventional receptacle can only be made to 0.4 m/m so that it is not suitable to test a printed circuit board with a gap less than 0.4 m/m between two points.